This invention relates to the recovery and conversion by reforming of petroleum oils front both shallow and deep deposits.
With the traditional method of extraction and recovery of ultra heavy tar, only deposits accessible to open-cast mining could be mined conventionally, the tar being heat-extracted in retorts after having been excavated from the mine pit. None of the existing methods can perform any conversion (reforming) of the oil at the mining site to allow the pumping of an oil product into a transport pipeline. Furthermore, none of the existing methods of thermal or chemical recovery can liquefy and extract any substantial amount of ultra heavy hydrocarbons from the deposit, without violating the economic-basis of the mining operation.
A number of attempts have been made to achieve so called viscosity reduction in order to increase the mobility of the hydrocarbons in the formation, thereby enabling them to be withdrawn by conventional techniques, such as natural flow, pumping, etc. The most popular method has been to reduce the viscosity of the hydrocarbons by elevating the temperature, in consequence of introducing thermal energy by a wide variety of means, such as hot water, in situ combustion, steam, heated natural and combustion gases and chemicals convertible into high pressure hot gases. Some of those techniques have received limited application in the recovery of medium heavy oil, API gravity in a range between 10.degree.-22.degree., with viscosity not much greater than 200 cp (both at 60.degree. F.) (16.degree. C.) and for a deposit with a medium thickness of 50-100 feet (15-30 metres).
The so-called medium-heavy oils just referred to are, by their nature, mobile to a degree in the deposit, but their velocity of gravitational mobility is very low and can be increased by decreasing their viscosity. Two basic thermal techniques of recovery are known for these medium-heavy-oils.
One technique is usually referred to as "steam-drive", wherein steam is continuously injected into a formation by means of an injection well. The injected steam heats the formation and medium-viscous hydrocarbons and drives the heated hydrocarbons toward one or more adjacent vertical production wells which are employed to withdraw them to the surface. There are the strict conditions limiting this kind of steam driving process, such as:
a) the formation must not be plugged by the gradually cooling products, which means that the natural non-heated oil ought to be light and mobile enough by itself to avoid its solidification when it cools. PA1 b) the permeability of the formation should be high enough to allow penetration of the steam, despite the fact that hydrocarbon material is consolidated in the pores. PA1 c) the pressure of the steam and its temperature should be sufficiently high to allow deep penetration into the formation. PA1 a) hot flue gases obtained from the combustion of fuel at high temperature and pressure; and PA1 b) a hydrogen donor solvent liquid; and raising the hydrocarbons thereby mobilized and liquefied by gas lift.
Even when these conditions are fulfilled, only a small portion of the medium-heavy-crude, and rather its light fraction only, can be mobilized and extracted by the steam-drive system, and only from the very upper part of the formation, where the steam has a natural tendency to sweep around the injection well. The lower part of the deposit in general remains unheated and worse, becomes impregnated with the previously heated heavier fractions of the oil from the upper part of the formation that have descended and cooled in the lower part of the formation. As a result, the lower part of the formation is converted into strata that are nonpermeable to any heat carriers, and remains lost as regards further recovery processes.
An alternative to "steam-drive" is "hot water drive" which, in one of the most advanced processes (U.S. Pat. No. 4,305,463) employs a flushing medium injected in a series of pressure pulses to force the heated fluids through the pores by hydraulic ramming. However, despite dramatic improvements in the effect of "driving" the hydrocarbons through the formation pores, the method still has application to light and medium heavy oil!s only, and cannot be used for ultra heavy tars and asphalts.
In the second basic technique, commonly referred to as single well injection or "huff and puff", steam, heated gases, combustion gases, or a combination of them is injected into the formation through a single injection well in a batch quantity for a selected period (huff phase). The formation is allowed to "soak", during which time the heat permeates, heating a larger volume of the hydrocarbon reservoir, and the heated mobile hydrocarbons are supposed then to be withdrawable from the formation through the same well during an extraction period (puff phase).
The "huff and puff" technique has arisen due to the known inefficiency of the steam and hot water driving methods, in an attempt to deal with heavier oils and thicker deposits. However, this process basically contradicts the logic of the use of driving forces in the formation, as commonly applied in the production of liquids from boreholes; it delivers small quantities of melted, heated product, and only in the case of a formation thick enough to allow some product to flow into the injection well from the inverted cone region of the formation that is heated by the injection and soak. The major portion of the heated, melted hydrocarbon is repelled in the "huff phase" into peripheral parts of the well region where it impregnates, solidifies in and plugs the pores of the formation.
There are processes which include so-called "enhanced recovery" techniques employing different chemicals and agents, all of them aiming to achieve better mobility of the oil by gravitational and/or pressure forced flow of liquids. The majority of these techniques are orientated towards decreasing surface tension between oil and water phases, and/or decreasing the oil viscosity in the formation. Some of these known techniques have limited use in the recovery of medium-heavy-crude under certain conditions. However, despite all these efforts the majority of the oil-bearing formations all around the world are known to contain enormous reserves of heavy and ultra-heavy hydrocarbons from which the crude cannot technically and economically be recovered in large quantities by the employment of any known process. None of the known processes is able to provide any improvement in the mobility of ultra-heavy crude or any reforming and conversion of ultra-heavy crude into a lighter product i.e. of pipeline quality--at the well site.
A useful steam generating system is described in U.S. Pat. No. 4,930,454. In that patent is described a method for catalytic combustion of heavy topped Kern fuel oil (13.degree. API) as a fuel for steam generation. It was the claimed and experimental intent of the inventors of that patent to provide stoichiometric oxygen for the fuel as the admixture passed over the catalysts for catalytic combustion. The catalyst temperature was carefully controlled within the operating stability range by the addition of liquid water upstream of the catalyst.
Although other diluents are mentioned as useful in admixture described in that patent, the specific example directed to such a heavy fuel oil indicated that water was added to the oil on a 14:1 by weight ratio to obtain a 99.7% carbon conversion to CO2 ("complete combustion" claimed and described therein). It appears that using any of the other diluents, all of which were gas, could not possibly meet the requirements of the invention, i.e., the extreme dilution of the reactants by performing catalyst temperature control using sensible heating of gas would prevent reaction within an economically volume of catalyst. The skilled person would decide not to endeavor to experiment with such easily predictable failure.
It is an object of the present invention to recover ultra-heavy and heavy hydrocarbons and tars, particularly crudes having API gravity below 15.degree. (at 60.degree. F.), from consolidated or non-consolidated formations having low to very high relative permeability to oil, gas and water.